Weather – October 2006, Vol. 61, No. 10 278 Peter Brimblecombe 1 Carlota M. Grossi 1 Ian Harris 2 1 School of Environmental Sciences University of East Anglia Norwich 2 Climate Research Unit University of East Anglia Norwich Architects from Sir Christopher Wren onwards have worried about the impact of time, smoke and weather on their buildings. Over the last century climate has often seemed less important than air pollution as a determinant of damage. The reduction in acidic air pollutants in urban areas in recent years has meant that frost, rain or wind can become more dominant as weathering processes than in the recent past. Although the predicted changes in temperature or precipitation seem small they can be ampli- fied in some mechanisms of damage. Britain has a damp climate. This has been a lament since Roman times, when Tacitus was able to write that the British Isles were cloudy with frequent rains, but never bitterly cold. Such meteorological character- istics have important implications for the interaction of our buildings with their environment. While being damp, the climate is more temperate than in the con- tinental Europe, so frost damage or the weight of snow on roofs has never been quite as important as, for example, in the European interior. Frequently, floods (Lanza 2003) and changes in the water table (Sauer 2005) damage heritage and archaeological sites such as Blickling Hall in Norfolk (see Fig. 1), but this paper concentrates on the dampness in terms of water vapour and rainfall rather than flooding. It considers the impact of changes in dampness that is likely to have an effect on buildings and the way the fabric may be sensitive to damage. In particular, we concentrate on how humid conditions can promote the decay of wood and mobilisation of salts, in addition to the role that wet surfaces play in enhancing the deposition of pollutants. Dry conditions can also affect building fabric through excessive moisture loss from unfired building materials, or more structural problems that can arise when soils dry out. Data sources and methodology The long climate record available for England, most notably as the Central England Temperature (CET) record (Manley 1974; Parker et al. 1992) and the rainfall records of Craddock and Wales-Smith (1976), allows our analysis to be taken back to the eighteenth century. The temperature data used here comes from this CET record, originally assembled by Gordon Manley, but now maintained at the Hadley Centre in the UK. This consists of daily temperatures back to 1772 and monthly averages back to 1659. The homogenised data are adjusted to represent the climate of central England often seen as representative of the climate in the region between Oxford and the Lancashire plain. A parallel set of data was assembled for rainfall by Craddock and Wales-Smith for the East Midlands and covers the years 1726 to 1975 with a series for England and Wales from 1766 (Wigley and Jones 1977). A number of useful addi- tional datasets have been derived from these records, most notably the evapo- transpiration and ultimately soil moisture deficit (e.g. Wigley and Atkinson 1977). The increasing availability of modelled output for the twenty-first century allows us to consider future changes in meteoro- logical parameters, and here we use the output from the Hadley model (HadCM3, a coupled ocean-atmosphere global circu- lation model from the Hadley Centre (Johns et al. 2003)). The analysis of future trends has relied mostly on the A2 scenario (IPCC SRES Emissions Scenarios – Version 1.1 (July 2000)). This scenario describes a very hetero- geneous world in which the underlying theme is that of strengthening regional cul- tural identities, with an emphasis on family values and local traditions, with high popu- lation growth. It gives pronounced changes in future climate, so should result in strong signals in terms of future pressures on archi- tectural heritage. The A2 emissions scenario sees high energy and carbon usage, giving The effect of long-term trends in dampness on historic buildings Fig. 1 General view of the front of Blickling Hall after the flood event of 2001 © By kind permission of David Kirkham, Fisheye Images, Norfolk